Compound-two-stage resilient isolation mounting for use in attenuating mechanical vibrations

ABSTRACT

The invention is a resilient isolation mount to be used between vibrating objects and their supporting structures to reduce the transmitted vibration.

0 United States Patent 1191 I [11 3,764,100 Young et a1. Oct. 9, 1973COMPOUND-TWO-STAGE RESILIENT {56] References Cited ISOLATION MOUNTINGFOR USE IN UNITED STATES PATENTS ATTENUATING MECHANICAL 2,926,881 3/1960Painter 248/358 R VIBRATIONS 2,295,829 9/1942 Carlson 248/358 R3,128,978 4/1964 Sykes 248/358 UX [75] lnventors. William I. Young,Elkndge, Robert J Hanna's Edgewater' both of Md- 2.83( ),780 4/1958Schloss 248/22 [73] Assignee: The United States of America as FOREIGNPATENTS Q APPLICATIONS represented y the Secretary of the 142,244 7/1951Australia 188/1 B Navy, Washington, DC. I Primary ExammerRoy D. FrazierFlledi 1971 Assistant Examiner-Richard L. Stroup [2 App]. N03 212,358Alt0rneyR. S. Sciascia et a1.

[57] ABSTRACT g The invention is a resilient isolation mount to be used[58] d 9 l 5 22. between vibrating objects and their supporting strucle8 tures to reduce the transmitted vibration.

4 Claims, 4 Drawing Figures Patented Oct. 9, 1973 FIG.

Patented Oct. 9, 1973 2 Sheets-Sheet 1:

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SIMPLE MOUNT ---COMPOUND MOUNT l2 DB OCTAVE 24 DB/OCTAVE/ LOGLU ICOMPOUND-TWO-STAGE RESILIENT ISOLATION MOUNTING FOR USE IN ATTENUATINGMECHANICAL VIBRATIONS The invention described herein may be manufacturedand used by or for the Government of the United States of America forGovernmental'purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION The invention is acompound mount having a seismic mass and resilient elements arranged ina balanced" configuration; i.e., one in which the elastic center of themount coincides with the center of gravity of the seismic mass-desirablefor decoupling the remaining five modes of vibration of the seismic massfrom the mode of exitation as well as minimizing shock excursions.

OBJECTS OF THE INVENTION It is a primary object of the instant inventionto achieve a more efficient vibration isolator than is possible withsimple (one-stage) resilient mounts.

It is a further object of the instant invention to provide a mount witha transverse spring rate no greater than the axial spring rate.

It is yet another object of the instant invention to provide a mountwhich is self-snubbing or captive such that if the mount should besubjected to extreme forces, the mount would be restrained by metalrather than by the resilient portion of the mount.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows the instant invention witha quartersection removed;

FIGS. 2 and 3 are schematic representations of simple and compoundmounting systems FIG. 4 shows typical transmissibility curves for simpleand compound mounting systems having the same fundamental naturalfrequency.

DESCRIPTION OF THE PREFERRED EMBODIMENT The principles and theory of thecompound mount 7' are well known and likewise its superior isolationability compared to a simple mounting of comparable fundamental naturalfrequency. One indicator of mount,

performance is the transmissibility (see FIGS. 2 and 3) which, for amount attached to a rigid foundation and supporting a load, is the ratioof transmitted force to applied force, expressed as a logarithm.Theperformance of a simple mounting at best approaches that of anidealized" spring, i.e., at frequencies well above the naturalfrequency, the transmissibility decreases at a rate of 12 decibels peroctave change in exciting frequency. This compares with a rate of 24decibels per octave for a compound mounting at frequencies above thesecondary natural frequency (see FIG. 4). Thus, as the excitingfrequency increases, the compound mount rapidly becomes a far moreeffective isolator than the simple mounting.

Referring to FIG. 1, the invention is constructed in two identicalsections, each consisting of a seismic mass 10, resilient element 16,and support plate or mounting means 14. To assemble, the sections areplaced with their support plates 14 together and the seismic masses 10are bolted together through the spacer yokes 12 via openings 24 to forma single rigid seismic mass. A preload or support means spool,consisting of tube 18, end cap 26, and threaded upper flange 20, is usedto support the load. The spool is inserted through the resilient element16 and the threaded upper flange 20 is screwed down to obtain a desiredpreload. As shown in FIG. 1, the resilient element 16 engages thepreload spool only near the ends of the spool. This invention is thenused in a manner identical to simple mountings. It

is supported by the ears of the support plate 14 havingengagessubstantially completely one side of the upper surface of the secondseismic element 10'. The portion of the yokes between the upper andlower planar sections surround the plane of engagement of the supportplates and resilient elements. As shown and described, the supportplates are free to move upon deflection of the resilient elements butthe plates would be confined by the yokes, seismic masses and bolts uponfailure and destruction of the resilient means. The yokes are attachedto the seismic masses by means of long bolts 24 which pass through themasses and the yoke.

The result is aunique arrangement of seismic mass with respect to thesupport plates which allows the mount to be balanced, i.e., the elasticcenter of the mount coincides with the center of gravity of the seismicmass, virtually decoupling all five remaining modes of vibration of theseismic mass from the mode of excitation. The mount is compact, havingresilient elements concentrically within the seismic mass yet preservingaccess to the support plates thereby allowing a much more compact mountthan could otherwise be achieved. The instant mount is captive, i.e.,the spacer yokes make the seismic mass captive with respect to the loadplate while the flanges of the preload spool restrain it with respect tothe seismic mass, so that the entire mount is self-snubbing.Furthermoreflhe mount is symmetric about the plane of the support plateand so can be loaded from either direction along its central axis. Ithas'a low radial stiffness for good isolation of vibrations in theradial direction. The mounting is in two symmetric halves so that asingle mold could be used to manufacture as well as to permitdisassembly for inspection or maintenance. The seismic mass iscompletely accessible so that mass can be added to or removed from itfor purposes of changing its natural frequency.

The present invention may be constructed utilizing mild steel for thepreload spool, seismic mass and support plates, and a neoprene rubberfor the resilient elements. The use of alternative elastomers is notprecluded.

It is understood that the invention is not limited to the exact detailsof construction shown and described for obvious modifications will occurto persons skilled in the art. It is therefore to be understood thatwithin the scope of the appended claims the invention may be practicedotherwise than as specifically described What is claimed is: l. Acaptive vibration isolation device, comprising: a first resilientelement with an inner and an outer end face; a longitudinal bore throughsaid first resilient element; a second resilient element substantiallyidentical to said first resilient, said first and second resilientelements mutually engaged end to end to form a resilient unit symetricalabout the plane of engagement; an end cap;

a longitudinal preload spool within said bore, said spool having a firstand second end, said first end being flared for fixed engagement withthe outer end of said second resilient element, said preload spool endbeing threaded to engage said end cap;

a first seismic mass attached to said first resilient element;

a second seismic mass attached to said second resilient element;

a pair of spacer yokes rigidly engaging said first and second seismicmasses to form a loose noncontacting enclosure surrounding the engagedends of said first and second resilient elements; a first support plateengaging said first resilient element and partially within said spaceryokes; and, a second support plate substantially identical to said 5first support plate and mutually engaging said first support plate andengaging said second resilient eleinent.

2. A captive vibration isolation device, as in claim 1, wherein: V i

said resilient unit engages said preload spool only near the ends ofsaid spool.

3. A device as in claim 1 wherein said seismic mass is concentricallymounted with respect to the longitudinal axis of the preload spool andsymmetrically mounted with respect to said support plates.

4. A captive vibration device, comprising:

a first and second resilient means to isolate a vibrating mechanicaldevice;

a preload spool means centrally located within each of said first andsecond resilient means for engagement with a vibrating mechanical deviceand capa- -ble of simultaneously longitudinally compressing said firstand second resilient means;

a first and second external seismic mass whose combined center of massis located at the combined center of vibration of said first and secondresilient means said first and second seismic mass engaging the surfaceof said first and second resilient element;

a pair of spacer yoke means for separating and rigidly connecting saidfirst and second seismic mass means; and

a first and second support plate means for engaging the combinedresilient means at its center to sus- 3 5 pend a vibrating mechanicaldevice.

a t a: t n

1. A captive vibration isolation device, comprising: a first resiLientelement with an inner and an outer end face; a longitudinal bore throughsaid first resilient element; a second resilient element substantiallyidentical to said first resilient, said first and second resilientelements mutually engaged end to end to form a resilient unit symetricalabout the plane of engagement; an end cap; a longitudinal preload spoolwithin said bore, said spool having a first and second end, said firstend being flared for fixed engagement with the outer end of said secondresilient element, said preload spool end being threaded to engage saidend cap; a first seismic mass attached to said first resilient element;a second seismic mass attached to said second resilient element; a pairof spacer yokes rigidly engaging said first and second seismic masses toform a loose noncontacting enclosure surrounding the engaged ends ofsaid first and second resilient elements; a first support plate engagingsaid first resilient element and partially within said spacer yokes;and, a second support plate substantially identical to said firstsupport plate and mutually engaging said first support plate andengaging said second resilient element.
 2. A captive vibration isolationdevice, as in claim 1, wherein: said resilient unit engages said preloadspool only near the ends of said spool.
 3. A device as in claim 1wherein said seismic mass is concentrically mounted with respect to thelongitudinal axis of the preload spool and symmetrically mounted withrespect to said support plates.
 4. A captive vibration device,comprising: a first and second resilient means to isolate a vibratingmechanical device; a preload spool means centrally located within eachof said first and second resilient means for engagement with a vibratingmechanical device and capable of simultaneously longitudinallycompressing said first and second resilient means; a first and secondexternal seismic mass whose combined center of mass is located at thecombined center of vibration of said first and second resilient meanssaid first and second seismic mass engaging the surface of said firstand second resilient element; a pair of spacer yoke means for separatingand rigidly connecting said first and second seismic mass means; and afirst and second support plate means for engaging the combined resilientmeans at its center to suspend a vibrating mechanical device.